1. Field of the Invention
The present invention relates generally to a system for actuating downhole tools in response to a pressure differential.
2. Description of the Prior Art
The basic function of most downhole tools involves surface manipulation of a downhole operation system to accomplish a task such as opening a valve, for example the opening and closing of a tester valve or a circulation valve.
This process usually involves a linear actuator, i.e., a power piston, which works off a pressure differential acting across a hydraulic area.
There are several ways in which this pressure differential can be achieved to operate such a linear actuator.
One technique is the use of a nitrogen charged system in which the nitrogen acts as a spring which supports hydrostatic well annulus pressure, but which can be further compressed with applied pressure at the surface allowing linear actuation across a hydraulic area downhole. An example of such a tool is seen in Ringgenberg U.S. Pat. No. 4,711,305 to Ringgenberg.
Yet another system provides first and second pressure conducting passages from either side of the power piston to the well annulus. A metering orifice type of retarding means is disposed in the second pressure conducting passage for providing a time delay in communication of changes in well annulus pressure to the second side of the power piston. Accordingly, a rapid increase or rapid decrease in well annulus pressure causes a temporary pressure differential across the piston which moves the piston. An example of such a system is seen in Beck U.S. Pat. No. 4,422,506.
Still another approach is to provide both high and low pressure sources within the tool itself by providing a pressurized hydraulic fluid supply and an essentially atmospheric pressure dump chamber. Such an approach is seen in Barrington et al U.S. Pat. No. 4,375,239.
Another approach is to utilize the well annulus pressure as a high pressure source, and to provide an essentially atmospheric pressure dump chamber as the low pressure zone within the tool itself. Such an approach is seen in Upchurch U.S. Pat. Nos. 4,796,699; 4,856,595; 4,915,168; and 4,896,722.